The paper investigates the mechanical and microstructural properties of friction stir welded joints of dissimilar aluminum alloys. The square tool was used to perform the friction stir welding operation. The maximum tensile strength is obtained at rotational speed of 800 rpm and welding speed of 30 mm/min. It was found that with the increase in tool rotational speed, tensile strength of welded joint increased at 800 rpm. At tool rotational speed of 800 rpm, the tensile strength decreased with increase in welding speed. The microhardness of friction stir zone decreased with decrease in welding speed. The microstructure revealed a dense welded zone without any defect. It was observed that the weld material was defect-free.

Description

Friction stir welding is a very significant welding invention, in which the deformation is imparted in the work material with the help of rotating pin and the shoulder
(Liu et al., 1997; Mishra and Ma, 2005; and Nandan et al., 2008). In friction stir welding, melting does not occur during the process, and the resulting joint has fine grained structure without any gas porosity (Singh et al., 2013; Bahrami et al., 2014a; and Çam and Mistikoglu, 2014). It is performed without the use of any filler material (Bahrami et al., 2014a and 2014b; and Çam and Mistikoglu, 2014). Friction stir welding has become an interesting topic of research in recent times. Many researchers have investigated the mechanical and microstructural properties of joints developed by this process. Chen et al. (2014) investigated the properties of joints of aluminum alloy and steel. Liu et al. (2003) performed the friction stir welding of 2017-T351 aluminum alloy, determined the optimum welding parameters and investigated the tensile properties of the welded joint. The authors concluded that the tensile properties of the welded joints were significantly affected by the friction stir welding process parameters. The microstructural analysis revealed that joints were fractured at the interface of weld nugget and interface. Sato et al. (1999) characterized the microstructure of friction stir welded 6063 aluminum alloy. It was found that there was a softened region in the weld, which consisted of fine grains created after recrystallization during the welding process. It was also found that precipitation sequences in the softened zone were due to thermal aging.